Current federal and most state regulations require automobile emission tests according to a defined procedure on a regular basis. These tests are conducted either at a government operated test facility or at designated private facilities. In addition, the increased interest in emissions as they effect air quality has resulted in substantial laboratory and field research into combustion by-products, particularly those from fossil fuel combustion.
Combustion emissions, especially those from motor vehicles, are normally tested for total unburned hydrocarbons, carbon monoxide, carbon dioxide, and oxides of nitrogen. Testing methodology includes non dispersive infrared (NDIR) for carbon monoxide and carbon dioxide, chemiluminescence (CLD) for oxides of nitrogen and flame ionization detection (FID) for unburned hydrocarbons.
In many areas of the United States vehicle emission testing equipment can comprise the so-called "repair grade" analyzers which, although of relatively modest price, are also of moderate accuracy and are used primarily for raw exhaust measurements. Repair grade analyzers are not suitable for more accurate emission testing. The Environmental Protection Agency has published guideline procedures, emission standards and equipment specifications for inspection and maintenance (I/M-240) equipment as set forth in EPA-AA-EPSD-IM-93-1 specifications dated April 1994 relating to high tech I/M procedures, emission standards, quality control requirements and equipment specifications. These specifications require instruments having much higher sensitivities (0-50 ppm) and have complex linearity, temperature and long term stability and interference specifications. Such instruments are referred to herein as "research grade" instruments. Higher sensitivity analyzers and procedures requiring the use of such analyzers are currently required in areas of the United States, deemed non attainment, i.e. with excess air pollution levels. This equipment is expensive, difficult to maintain and requires a relatively large installation and operation area and a high volume of tests to justify the expense. Small laboratories and small emission test facilities find it very difficult to justify purchasing such equipment and many do not have the space necessary or the test volume to operate such equipment.
Accordingly it would be desirable to have compact, portable emission testing equipment suitable for use in small testing facilities and laboratories that is relatively inexpensive and that produces results comparable to the I/M-240 equipment.